1. Field of the Invention
The present invention relates to a method and apparatus for improving a Discontinuous Reception (DRX) functionality, and more particularly, to a method and apparatus for handling a timer of the DRX functionality and a measurement gap in a user equipment (UE) of a wireless communication system, so as to enhance system scheduling efficiency.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
In LTE system, Discontinuous Reception (DRX) functionality is applied to MAC layer for allowing a user equipment (UE) to enter a standby mode during certain periods of time and stopping monitoring a Physical Downlink Control Channel (PDCCH), so as to reduce power consumption of the UE.
According to related protocol specifications, the DRX functionality is configured by Radio Resource Control (RRC) layer, an upper layer of RLC layer. If the DRX functionality is configured, whenever a new DRX cycle begins, an On Duration Timer is started and the UE is awaked to monitor the PDCCH until the On Duration Timer expires. In addition, when a DRX Inactivity Timer or a DRX Retransmission Timer is running, the UE also monitors the PDCCH to acquire information about whether the network has assigned resources for uplink transmission or whether the network has downlink data for the UE to receive.
During the time when the UE monitors the PDCCH, if the PDCCH indicates the UE to receive or transmit a new transmission packet, the DRX Inactivity Timer is started or restarted for allowing the UE to continue monitoring the PDCCH, so as to prevent missing reception or transmission of following packets or to reduce data transmission delay.
On the other hand, if the PDCCH indicates the UE to receive a packet but the packet cannot be decoded successfully on a Downlink Share Channel (DL-SCH), the MAC layer of the UE would perform a Hybrid Automatic Repeat Request (HARQ) process to request a retransmission of the packet. Since the UE would not receive any retransmission packet during a signaling round trip time (RTT) of the HARQ process, a HARQ RTT Timer is thus configured by the DRX functionality to allow the UE to enter into the standby mode during this round trip time. So the power consumption of the UE can further be saved.
After the HARQ RTT Timer expires, the DRX Retransmission Timer is started by the DRX functionality to awake the UE to start monitoring the PDCCH for detecting the retransmission packet of the HARQ process. In such a situation, if the retransmission packet of the HARQ process is successfully decoded, the DRX Retransmission Timer is stopped. Otherwise, the DRX Retransmission Timer is kept running until expiration, at which time the UE enters into the standby mode again.
In other words, the UE configured with the DRX functionality is allowed to stop monitoring the PDCCH during some period of time. The situations that the UE monitors the PDCCH when the DRX functionality is configured are summarized as follows: (1) when the On Duration Timer is running; (2) when the DRX Inactivity Timer is running; and (3) when the DRX Retransmission Timer is running. It is noted that the said timers and parameters used for controlling operation of the DRX functionality are configured by the RRC layer. Detailed operations of the DRX functionality can be referred to related specifications, and are not further narrated herein.
According to the current specifications, the said timers for controlling the DRX functionality may be overlapped with a measurement gap, i.e. a duration the RRC layer assigns to the UE for performing radio measurement. Since the UE is incapable of monitoring the PDCCH within the measurement gap, the network scheduling would be greatly limited if overlap occurs between the said timers and the measurement gap.
For example, if the DRX Retransmission Timer is overlapped with the measurement gap, the time that can be used by the network to schedule retransmission packets is reduced during the running time of the DRX Retransmission Timer, or even there is no chance for the network to schedule retransmission packets during the running time of the DRX Retransmission Timer. As a result, the network scheduling is greatly limited. Similarly, the problem may also occur to the DRX Inactivity Timer and the On Duration Timer.